Manatees live in warm coastal waters and require water temperatures warmer than about 68ºF (18ºC) (Reep & Bonde, 2006). Their ability to regulate their internal body temperatures is limited and thus they seek warmer water refuges during periods of cold weather. In Florida, which is in the northernmost extent of the manatee’s natural range, cold winter water limits their ability to survive year round in open water. The seasonal variability of water temperature is the most important factor driving manatee migration patterns (Haubold et al., 2006). For centuries, prior to the extensive urbanization of Florida’s coastal regions, manatees have sought refuge in naturally occurring sources of warm water. In winter, they migrate to warm water aggregation sites such as large natural springs, where the water maintains a constant temperature, and protected coves in the southerly parts of their range. Nowadays, warm water outflows from power plants also attract hundreds of manatees (Reynolds III, 1996; Shane, 1984). The fact that manatees have become habituated to many artificial warm water sources is a significant issue in the overall status of manatees, but less so when establishing protection zones.
Figure. Biologist photographing manatee scar patterns at Fort Pierce power plant, Florida
(photo: USGS – Sirenia Project).
With the development of coastal urban areas in Florida, a new source of warm water, the heated waste water discharged from power plants and industrial plants, became available for manatees to use in winter. The new source helped to expand the winter range for manatees in Florida by providing additional refuge sites during cold winter months. It is now common to see hundreds of manatees congregating around the discharge areas of power plants in winter. The difficulty for resource managers is the danger that any interruption in the operation of the power plant could cause harm to manatees that are habituated to these sites. Should a power plant close down during a cold snap, several dozens of manatees could be killed from the cold. Likewise, maintaining substantial flows of spring water during winter months is important for the manatee survival. Any changes to the configuration of this network of warm water refuges, to which manatees are now habituated, present a serious threat to the long-term survival of the Florida manatee (Haubold et al., 2006; U.S. Fish and Wildlife Service, 2001).